Mountain waves over the Alps

Mountain waves over the Alps

10 November 2015 06:00–07:50 UTC

Mountain waves over the Alps
Mountain waves over the Alps

High-level orographic cloud pattern occurred in the lee side of the Alps, gradually seen as a pronounced feature in the Convection RGB loop, along with the rising Sun.

Last Updated

29 October 2020

Published on

10 November 2015

By Ivan Smiljanic (DHMZ )

During sunrise high level mountain waves became easier to distinguish from the rest of the clouds in the Meteosat Convection RGB imagery, animation from 10 November 06:00–07:50 UTC and Figure 1.

Meteosat-10 Convection RGB, 10 November 09:00 UTC
Figure 1: Meteosat-10 Convection RGB, 10 November 09:00 UTC
Land Surface Temperature
Figure 2: Meteosat-10 Day Microphysics RGB, 10 November 09:00 UTC

The reason for that is the green component of the same RGB composite that includes a Sun reflection contribution in the 3.9 µm microphysical channel of SEVIRI instrument.

This also applies to the Day Microphysics RGB composite (Figure 2) which, even more so, has only the reflected component of the 3.9 µm channel (thermal Earth’s contribution extracted).

In the morning hours reflection from the very small ice particles, typical for high mountain waves, becomes gradually stronger. Reflection from the rest of the ice clouds naturally becomes gradually higher as well, but small ice particles always reflect much more.

Figure 3: Meteosat-10 Airmass RGB, 10 November 09:00 UTC
Figure 3: Meteosat-10 Airmass RGB, 10 November 09:00 UTC
Figure 4: Meteosat-10 Natural Colour RGB, 10 November 09:00 UTC
Figure 4: Meteosat-10 Natural Colour RGB, 10 November 09:00 UTC

From the Airmass RGB image (Figure 3) over the whole of Europe one could deduce the presence of the high-level north-westerly flow over the eastern Alps. This flow is responsible for the formation of observed wave cloud on the lee side of the mountains. This cloud looks very bright white in this RGB composite.

When we compare the different RGB combinations (Figure 1–4) it is obvious that the best contrast for wave clouds is given with the Convection RGB.


Previous case study

High-level mountain wave cloud over Pyrenees (2 July 2015)